Inula L.
As traditionally understood, Inula is a genus of ca. 90-100 species. Most are native in Eurasia, some in Africa. Three species are native in Belgium as well: Inula britannica L., I. conyzae (Griesselich) Meikle and I. salicina L. Inula conyzae is recently spreading in Belgium and now occurs in man-made habitats (old walls in cities, abandoned railway yards, coalmine heaps) outside its native distribution range. Both other species are seriously endangered in Belgium. A fourth species, Inula crithmoides L., a native of saline coastal habitats in southern and western Europe is slightly progressing to the north and reached the Netherlands in 2006 (Kers & al. 2008, Holverda & al. 2009). Its discovery in Belgium in the near future is possible. It is easily distinguished from all other Belgian representatives of the genus (native and alien) by its fleshy leaves.
Inula is a popular genus in cultivation. Akeroyd & al. (2000) cite 22 species (incl. Dittrichia viscosa) that are cultivated in Europe. See also Jäger & al. (2008) and Köhlein (2010).
The generic boundaries of Inula and its relationship with other genera require additional research. Recent molecular studies show that "the Inula complex" is a monophyletic group that also comprises all species of, among others, Telekia (England & al. 2009). Pending further studies both genera are here accepted in their usual circumscription.
1. Ligules absent or inconspicuous (less than 10 mm long). Capitulae numerous, ca. 6-10 mm across (native) === Inula conyzae
1. Ligules conspicuous, more than 10 mm long. Capitulae few, more than 10 mm across === 2
2. Capitulae 60-100 mm across. Outer involucral bracts ovate, obtuse at apex. Robust perennials, (60-) 90-200(-250) cm tall. Basal leaves up to 80 cm long === 3
2. Capitulae ca. 20-40 mm across. Outer involucral bracts oblong-lanceolate to linear, acute at apex. Smaller perennials, 25-75 cm tall. Basal leaves up to ca. 15 cm long (native) === I. britannica and I. salicina
3. Inflorescence corymbose and wide, most flowers pedunculate (peduncles widely diverging) === 1. I. helenium
3. Inflorescence racemose and narrow, most flowers sessile (if on peduncles, than these neatly appressed to the stem) === 2. I. racemosa
Additional aliens: Inula hirta L. (S, C and E-Eur., garden escape?) and I. spiraeifolia L. (syn.: I. squarrosa L.) (S-Eur., garden escape).
Literature:
Akeroyd J.R., Gardner M.F. & Knees S.G. (2000) Inula. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 550-554.
Anderberg A.A. (1991) Taxonomy and phylogeny of the tribe Inuleae (Asteraceae). Plant Systematics and Evolution 176: 75-123.
Ball P.W. & Tutin T.G. (1976) Inula. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 4. Cambridge University Press, Cambridge: 133-136.
Englund M., Pornpongrungrueng P., Gustafsson M.H.G. & Anderberg A.A. (2009) Phylogenetic relationships and generic delimitation in Inuleae subtribe Inulinae (Asteraceae) based on ITS and cpDNA sequence data. Cladistics 25(4): 319-352.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Köhlein F. (2010) Alant. Vielseitige Wildstaude. Gartenpraxis 12.2010: 20-24.
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Sell P. & Murrell G. (2006) Flora of Great Britain and Ireland. Vol. 4 Campanulaceae – Asteraceae. Cambridge University Press, Cambridge: XXVIII + 624 p.
Shekhar S., Pandey A.K. & Anderberg A.A. (2013) The genus Inula (Asteraceae) in India. Rheedea 23(2): 113-127. [available online at: http://www.iaat.org.in/Rheedea23_113-127.pdf]